There are present in wireless communications, particularly, in wideband transmission, not only a path through which a signal arrives early but also a path through which a signal arrives with a delay involved as a result of reflection on obstacles including buildings and mountains. An environment in which multi-paths are present is referred to a multi-path environment. For example, if a receiver apparatus performs a demodulation process on a received signal in a time domain, a channel impulse response is needed as a propagation channel in the time domain. If the receiver apparatus performs the demodulation process on the received signal in a frequency domain, a frequency response as a propagation channel in the frequency domain is needed. A method of transmitting a pilot signal from a transmitter apparatus to a receiver apparatus is available so that the receiver apparatus beforehand stores an amplitude value of a waveform (or a signal string) of the pilot signal to estimate the propagation channel. Statistical properties of the propagation channel, such power of a delay path, need to be known to obtain a high-accuracy propagation channel estimated value.
Non-Patent Literature 1 listed below describes a technique of reducing the effect of noise and interference and improving an estimation accuracy by selecting paths to be estimated in scattered pilot OFDM (Orthogonal Frequency Division Multiplexing). More specifically, in accordance with Non-Patent Literature 1, paths of high power are extracted from among channel impulse response that is approximated by performing IFFT (Inverse Fast Fourier Transform) to estimated values of frequency response, and a delay time corresponding to the path is used as a delay time of tap for use in estimation.
However, if the number of estimated frequency response is limited, this method causes an approximate channel impulse response obtained through IFFT to be spread in position from where the path is originally expected. In such a case, an increase in the estimation accuracy is subject to limitations because delay times that are around a path to be estimated and does not contribute to any increase in the estimation accuracy are also selected.
FIG. 1 illustrates a transmission model that is free from path spreading. The abscissa represents delay time and the ordinate represents power of path. There exist two paths, path 101 and path 102. Since paths having power above a threshold value 103 are selected, path 101 and path 102 are selected.
On the other hand, FIG. 2 illustrates spread paths. Path 101, path 102, and threshold value 103 are identical to those illustrated in FIG. 1. A spreading 201 of the path 101 and a spreading 202 of the path 102 cause paths 203 through 206 to be selected as paths above the threshold value that are redundant.
On the other hand, Patent Literature 1 listed below describes a technique in which an estimated value is calculated in accordance with a plurality of channel model structures and an optimum channel model structure is selected in terms of a separation or other factor between an estimated evaluation value and a received signal. Since this technique selects paths based on statistical information criterion rather than power, the problem of Non-Patent Literature 1 is reduced.